The present invention relates to a process for the identification of colors, in which a colored surface is scanned by electro-optical means to measure the presence of selected colors such as red, green, and blue and various other colors are defined by the use of predetermined ranges for the selected colors.
In U.S. Pat. No. 3,210,552, a device has been disclosed for identifying the presence of a color in a test sample by measuring the intensity of selected colors and performing measurements to determine if these intensities were within predetermined ranges. Three optical-electrical transducers were used according to the patent, each responding to a selected light-component of the sample. The output-signal of each transducer represented one of the selected colors and was coupled to a respective control circuit, which generated an output-signal only when the input-signal was within a predetermined and adjustable range. The output signals of the control circuits were transferred to a coincidence-circuit, the coincidence circuit furnished an output-signal only when all of the control circuits simultaneously furnish output-signals. The output-signal of the coincidence circuit indicated the presence of a certain color, that is, a color which is determined by the threshold values of the control circuit.
Thus, from the entire color-region, defined in three dimensional space by the selected colors, a relatively narrow color region with an adjustable volume and adjustable dimensions is defined. If the color of the sample lies within this region, it is identified.
A variant of this spatial color-identification is also described in the aforesaid patent. Instead of operating on a 3-dimensional basis, one can operate on a 2-dimensional basis. In this case, only two optical-electrical transducers are used. This entails the assumption that one of the selected colors is constant. Thus, the 3-dimensional signal processing becomes a 2-dimensional signal processing. The output signals of the transducers are connected to control circuits having adjustable threshold-values which are connected to a coincidence-circuit. An output signal occurs, that is to say the color is identified, when both control circuits furnish an output signal.
Thus, in this 2-dimensional case, one does not define and analyze a solid spatial element, but one eliminates a surface element, that is, the entire color-region is projected onto a plane in which the identification-surface is delineated.
It is furthermore stated in the aforesaid patent that for the identification of several colors, several such circuits with differently adjusted threshold values can be operated in parallel.
The technique of the delineation of specific partial surfaces in a color region reduced to two dimensions has been further developed in the U.S. Pat. No. 3,012,666. This patent describes an improved sorting-out of articles on the basis of their color; this being achieved with the aid of electronic color-identification. In this patent, a light-ray is reflected by the object under test and is split by means of a half silvered mirror into two partial rays, of which one is transferred via a red-filter and the other via a green-filter to separate optical-electrical transducers. In the simplest case, the colors are identified through illumination with monochromatic light, a procedure which is of no interest here. During the scanning with white light, the primary color-measuring-value-signals, which are furnished by the transducers, are evaluated by means of complicated thresholds, whereby the individual color-regions are delineated by means of several straight lines which, electronically, are reproduced through these adjustable thresholds.
This delineation leads to a more refined form of identification of the desired colors and is improved even more by closed areas being outlined by individual straight lines.
Subsequently, this concept also appears in the DT-OS 2,158,758 and DT-OS 2,404,201 (supplement to DT-OS 2,158,758. In the DT-OS 2,404,201, a coordinate-transformation of the original color-measuring-value-signal is carried out in addition; however, a projection of this converted coordinate-system is made on one of the principle planes and thereafter, the evaluation-system which is obtained in this manner and which possesses one less dimension than the transformed coordinate-system, is evaluated according to the known demarcation as figures lying in a single plane. In the case in which one works with three primary colors, this leads to a reduction of the identification-problem from the 3-dimensional color-region to 2-dimensions. This corresponds to the color-identification process according to the U.S. Pat. No. 3,210,552 and No. 3,012,666.
The types of color-identification processes described up to now which, in essence, are based on the reduction of the evaluation to 2-dimensions, have decisive disadvantages, as many cases of their application have shown. For example, in techniques used in the textile industry, colored sample copies such as textile-pattern designs which have been hand-painted by an artist are electro-optically scanned, in order to identify the color of the individual pattern copies in individual color fields or in color samples, and record this color as information on a data-carrier for the control of the weaving looms. In this process, in which many inadequate conditions arise, the above described identification method has furnished results which were not satisfactory. Tolerances of commercially available dyes or pigments, inaccurate manual application of colors, soiling of the white pattern-carrier through small spatterings of black color during the printing of the screen of the pattern-carrier of the untreated pattern-carrier, and painting over corrected places, all of which lead to wrong color-identification, and also fluctuations of the color quantity, are to be included among such typical shortcomings.
The present invention is therefore based on the task of indicating an improved process for the identification of one color of a colored sample, from among a large number of colors which are present, which -- in the case of an electro-optical scanning sample -- has a considerably greater freedom from errors.